In order to excite magnetically a rotor of a rotating electric machine, for example a turbine generator, it is need to supply a field current to a field winding. As means for this, a system in which a carbon brush is in sliding contact with a collector ring to supply current directly to a rotating body has been generally known.
FIG. 9 shows an example of a conventional structure of a rotor 100 of a general rotating electric machine using the above described collector ring. Collector rings 102A and 102B paired on positive and negative electrode sides are usually located in an outside of the machine on a side of the rotor 100 opposite to a directly coupled side thereof. The Collector rings 102A and 102B are insulated and held to a rotor main shaft 104 as a hollow rotor shaft through collector ring insulating cylinders 103.
Center hole copper bands 106A and 106B on the positive and negative electrode sides are arranged in a shaft center portion of the hollow rotor main shaft 104 in such a state that they are insulated from each other. The paired collector rings 102A and 102B are electrically connected respectively to the center hole copper bands 106A and 106B on the positive and negative electrode sides by connecting collector studs 110A and 110B penetrating respectively through holes 108A and 108B provided radially. And the center hole copper bands 106A and 106B are similarly connected to a field winding of the rotor 100 by connecting studs or the like, so that a field current is supplied to the field winding.
In particular, in a system in which an inside of an electric power generator is cooled by hydrogen, a hydrogen seal packing 112 is provided at a periphery of an outer projecting portion of each of the collector studs 110A and 110B connected to the center hole copper bands 106A and 106B. A hydrogen seal plug 114 is mounted in an opening of a center hole 104A of the rotor main shaft 104.
Although a drive system of the electric power generator shown in FIG. 9 has a drive device, such as a steam turbine, provided on only one side, there is another drive system of the electric power generator in which an electric power generator GN is driven by a steam turbine ST and a gas turbine GT from both sides of the electric power generator GN, as shown in FIG. 10.
In the both drive system, a transmission torque corresponding to a turbine output is applied to the rotor main shaft 104 on the side where the collector rings are located. Thus, torsional stress is produced in the rotor main shaft 104 on the side where the collector rings are located during the rotor main shaft 104 is driven as described above. When a short-circuit accident or the like occurs, an excessive torque is applied to the rotor main shaft 104 on the side where the collector rings are located.
In the structure of the rotor of the rotating electric machine shown in FIG. 9, since the through holes 108A and 108B exist radially in the rotor main shaft 104 as a hollow rotor shaft, torsional stress is concentrated around the through holes 108A and 108B in the rotor main shaft 104.
Although the through holes 108A and 108B are provided at portions of the collector rings 102A and 102B, it is difficult to increase a diameter of the rotor main shaft 104 because the outer diameters of the collector rings 102A and 102B are restricted by peripheral speeds of carbon brush sliding surfaces of the collector rings 102A and 102B.
Another conventional hollow collector shaft is formed independently from a rotor main shaft and coupled to the rotor main shaft by a coupling. A pair of center hole copper bands electrically connected to a pair of center hole copper bands of a center hole of the rotor main shaft is arranged in a center hole of the collector shaft. A pair of collector rings is fitted on both sides of a longitudinal central portion of an outer circumferential surface of this collector shaft, and the central portion has an outer diameter larger than that of each of the paired collector rings. In order to fit the pair of collector rings on the both sides of the longitudinal central portion of the outer circumferential surface of the collector shaft, the coupling for coupling the collector shaft to the rotor shaft is fitted to an end of the outer circumferential surface of the collector shaft by an shrinkage-fit.
A pair of radial through holes through which a pair of axial studs is inserted is formed in the central portion. The pair of axial studs extends from the pair of center hole copper bands of the center hole of the collector shaft to a pair of recesses of an outer circumferential surface of the central portion. The pair of collector rings is provided with a pair of lead bars longitudinally extending toward the pair of recesses. The pair of lead bars extends to outer ends of the pair of axial studs located in the pair of recesses in a pair of longitudinally extending grooves formed in the outer circumferential surface of the large-diameter central portion and is electrically connected to the outer ends of the pair of axial studs.
The conventional collector shaft makes the outer diameter of the central portion in which the through holes for the pair of axial studs are formed being larger than the outer diameter of the pair of collector rings to increase its strength to torsional stress. However, since the center hole and the pair of through holes extending radially remain in the collector shaft, the strength of the collector shaft to the torsional stress is still reduced. The work for shrink-fitting the coupling on the one end portion of the outer circumferential surface of the collector shaft is complicated. Further, the work for removing or shrink-fitting the coupling from or to the one end portion of the outer circumferential surface of the collector shaft is troublesome when each of replacement and repair of the pair of collector rings is performed.